Two quotes on who and what from Hannah Arendt:
No society can properly function without classification, without an arrangement of things and men in classes and prescribed types. This necessary classification is the basis for all social discrimination, and discrimination, present opinion to the contrary notwithstanding, is no less a constituent element of the social realm than equality is a constituent element of the political. The point is that in society everybody must answer the question of what he is — as distinct from the question of who he is — which his role is and his function, and the answer of course can never be: I am unique, not because of the implicit arrogance but because the answer would be meaningless.
The moment we want to say who somebody is, our very vocabulary leads us astray into saying what he is; we get entangled in a description of qualities he necessarily shares with others like him; we begin to describe a type or a “character” in the old meaning of the word, with the result that his specific uniqueness escapes us. This frustration has the closest affinity with the well-known philosophic impossibility to arrive at a definition of man, all definitions being determinations or interpretations of what man is, of qualities, therefore, which he could possibly share with other living beings, whereas his specific difference would be found in a determination of what kind of a “who” he is.